Induction heating apparatus



Sept. 25, 1956 H. E. GRENOBLE INDUCTION HEATING APPARATUS 2 Sheets-Sheet 1 Filed March 30, 1954 Inventor. Herbert E. Grenoble,

wi mh His Attornes.

i p 25, 1956 H. E. GRENOBLE 2,764,660

INDUCTION HEATING APPARATUS Filed March so, 195

2 Sheeis-Sheet 2 Inventor: Herbert E. Grenoble,

His Attorney.

United States Patent INDUCTION HEATING APPARATUS Herbert E. Grenoble, Ballston Lake, N. Y., assignor to General Electric Company, a corporation of New York Application March 30, 1954, Serial No. 419,771 6 Claims. (Cl. 219-1051) of induction heating become pronounced. One of these is the precise support of the induction coil with reference to the bore to maintain the induction coil out of contact with the surface being heated so as to eliminate arcing and wear of the coil. Another problem is to provide suflicient power to do the heating in the time required without overheating the coil or its leads which necessitates a minimum clearance between the coil and the bore as well as elficient power leads. Other problems are the creation of internal strains and distortions in the unhardened portions of the article and the provision of high accuracy and selectivity of the place of heating to produce an article having hardened surfaces closely limited to the area requiring it. Accordingly, it is an object of my invention to provide an induction heating apparatus which provides the solution of the aboveproblems.

It is another object of my invention to provide induction heating apparatus capable of localizing heating of high intensity to a narrow band in the axial direction along the surface of the bore whereby precise selectivity in the location of the hardened surface of an inner bore may be accomplished.

Still another object of my invention is to provide for accurately supporting and dimensioning an induction heating coil whereby a high efficiency of heating is accomplished.

A still further object of my invention is to provide an improved inductor having a low impedance power circuit to operate at low voltage and low voltage regulation.

It is also an object of my invention to provide an induction heating apparatus which will heat uniformly substantially to the end of a bore without the use of additional fixtures.

Further objects and advantages of my invention will become apparent and my invention will be better understood from the following description referring to the accompanying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In the drawings,

Fig. 1 is a fragmentary drawing, partially broken away, of one form of the improved inductor of my invention illustrating its use.

Fig. 2 is a perspective view of the inductor of Fig. 1.

Fig. 3 is a sectional view of the inductor of Fig. 1 along the line 3-3 of Fig. 2.

Fig. 4 is a perspective view of the inductor of Fig. 1 at an intermediate stage in its manufacture.

Fig. 5 is a fragmentary perspective view of a modified '2 form of my invention at an intermediate stage in its manufacture.

Fig. 6 is a fragmentary top invention shown in Fig. 5

In accordance with one embodiment of my invention, an inductor is provided with a single turn coil arranged in a plane perpendicular to the axis of the conductor and is mechanically supported from one end by means of a tapered shank formed of two closely spaced .D-section leads which may be accurately and quickly located in a tapered holder. The space between the two portions of the shank is filled with a cast resin material to serve as an electrical insulating spacer and a cast resin material is cast about the head of the inductor to make the induction coil rigid. The construction of the inductor is such that it may be easily fabricated and the coil machined to its final dimension with reference to the tapered shank so that the clearance between the inductor coil and the inner bore of the work piece being heated may be reduced to the minimum for high heating efliciency and heating localization without risk of contact between the coil and the work piece. In one form of the invention, the inductor coil is hollow and cooling ducts are provided within the D-shaped leads in communication with the interior of the .coil for the passage of coolant.

Referring to the drawing, I have shown in Fig. 1 the application of an inductor 1 made in accordance with my invention. The inductor 1 is provided with a tapered shank 2 which may be easily supported, as in a machine view of the form of my lathe, providing a holder 3 having a correspondingly tapered bore to accurately align the inductor with the work piece, such as internally splined gear 5, which it is desired to heat. The holder 3 is shown as comprising a pair of plates 3a and 311, secured together as by bolts 4. Plates 3a and 3b are electrically insulated from each other by sheet insulation 30 therebetween and insulating sleeves 4a around bolt 4. Gear 5 is shown as being mounted in accurate axial alignment with holder 3 for rotation in a chuck 6 to insure the uniform heating .of all points of the surface of a peripheral band of the bore.

Referring specifically to Fig. 2, it can be seen that tapered shank 2 comprises electrical leads 8 and 9 which are generally D-shaped in cross section and have their flat sides presented to each other across a narrow gap 14. Since the inductance between closely spaced parallel plates is small, this construction provides a low impedance circuit because most of the current will flow in that portion of the copper adjacent the flat faces of leads 8 and 9 due to the low inductance of that path. Consequently, the volt-age drop in the leads 8 and 9 is minimized by their design. Moreover, by utilizing a tapered shank 2, it is apparent that it is quite easy to accurately insert an inductor in a supporting holder 3 to provide rigid support for the inductor coil from one end eliminating the need for special support or alignment devices within the bore of the work piece.

As best shown in Fig. 4, the tapered shank 2 is connected through a reduced section 11 to the single turn coil 10. The single turn coil 10 is short in the axial direction so that the currents induced in the work surface are localized to heat a narrow band of surface substantially the width of the coil 10 to high intensity. This construction makes it possible to selectively heat sections along the bore of a work piece so as to precisely limit the heating to that portion of the surface required to be hardened or annealed. It also enables the uniform heating of the bore of the work piece substantially to the end thereof without the aid of an apertured extension on the work piece to carry the flux from the turns of a multiturn coil until all the turns have passed beyond the end. of the work piece.

A castable resin 13 fills the gap 14 between the leads 8 and 9 to provide electrical insulation and to fill the voids in the inductor head so as to produce a rigid unitary structure. Cast resin 13 also encircles reduced section 11 of the inductor to clamp the leads 8 and 9 together. Since this construction permits the machining of the taper on the shank 2 and the final outside diameter of the inductor coil 10 with reference to each other after casting, a high degree of dimensional accuracy is obtained to enable the inductor to be used with very small clearance between the inductor coil and the bore of the work piece. A plurality of threaded openings 17 are shown as be ng provided in conductor elements 8 and 9 1n communication with gap 14 so that the casting resin 13 additionally serves to hold leads 8 and 9 together.

In order to prevent the overheating oi the inductor, cooling means are provided. As shown in Figs. 3 and 4, inductor coil 10 is hollow as at 15 to provide for the passage of coolant therethrough. The conductor elements 8 and 9 are shown as providing hollow passages 16 in communication with the interior of inductor coil 10 to carry coolant. Coolant, such as water, is providedto passages 16 through conduits 1% which are shown as being secured in the threaded ends of passages 16.

In use, the tapered shank 2 of the inductor 1 is lnserted into the tapered bore of holder 3 to automatically precisely position the coil 10 with respect to chuck 6. A high frequency power source 7 is connected to plates 3:: and 3b of the holder 3 to provide high frequency power to the inductor. The gear, or apertured work piece, 5 to be internally hardened is supported for rotation in a chuck 6 which is in precise axial alignment with the holder 3. If desired, the chuck 6 or the holder 3 may be arranged for traversing movement so that any band of the interior surface of the gear 5' may be heated as required by being placed in radial alignment with the inductor coil 10. Due to the dimensional accuracy of inductor 1 and the resulting accuracy of its alignment with gear 5, the clearance e between the outer periphery of the inductor l and the interior splines of the gear may be in the order of .008". This small clearance enables a strong flux linkage between the inductor coil and the gear 5 so that a high efficiency of heating is obtained to quickly heat an internal surface Without tempering the portions of the gear overlying the splines. Further, the small clearance 2 serves to localize the heating to substantially the width of coil and variation in the scanning speed or rate of axial movement between the work piece and the inductor provides an easy means for varying the heating of immediately adjacent bands on the interior surface of the work piece.

Referring now specifically to Figs. 5 and 6, there is shown a modified form of my invention particularly adapted for the heating of interior bores having a diameter of 0.6 inch or less. Where the diameter of the inductor coil is large as compared to the radial thickness of the coil, the low mutual inductance between the outer portion of the coil and the work piece causes the greater percentage of the current to flow near the outer surface of the coil where it is more closely coupled to the work piece and hence more effective in inductively heating the bore of the work piece. As the ratio of the radial thickness of an inductor coil to the diameter of the coil increases, a larger percentage of the total current flowing through the coil passes through the portion of the coil near its inner surface because of the comparatively lower self-inductance of this path which more than offsets the low mutual inductance of the outer surface with the work piece. Consequently, in very small inductors it is desirable to reduce the radial thickness of the inductor coil. This is accomplished by the construction shown in Fig. 5 in which a solid inductor coil 20 of thin radial dimension is provided. Since inductor coil 20 does not incorporate a coolant path therethrough, other cooling means must he provided to prevent damage to the coil in use. As shown in Fig. 5, a cluster of axial tubes 21 are brazed, or otherwise secured, to the inner surface of the coil 20 in good heat conducting relationship therewith. Because they would short-circuit portions of the conductor coil 20 if connected directly to leads 8 and 9, tubes 21 are spaced a short axial distance from tubes 22 on leads 8 and 9 prior to casting the resin 13 to fill the voids in the inductor. In order to prevent the resin 13 from plugging up the openings between conduits 22 and the corresponding tubes 21, a small insulating sleeve 24 is inserted to bridge the gap therebetween. Upon casting, the cast material covers sleeve 24 and serves both to seal the joint between conduits 22 and tubes 21 and as an electrical insulator. If desired, conduits providing a high impedance to the flow of electric current may connect the free ends of tubes 21 to provide for the return flow of coolant to the supply. To eliminate the requirement for a plurality of coolant ducts through the conductor elements 3 and 9, manifolds 25 may be provided to distribute the water to the conduits 22. Thus the inductor coil 20 may be maintained at a cool temperature in a construction wherein the radial thickness of the inductor coil is very small as compared to the diameter of the inductor coil.

From the foregoing, it will be apparent that I have provided induction apparatus which is simple to manufacture, sturdy in construction, and which may be utilized in the eificient localized heating of interior surfaces.

While I have shown and described particular embodiments of my invention, further modifications and improvements will occur to those skilled in the art. I desire it to be understood, therefore, that my invention is not limited to the particular forms shown, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electromagnetic induction heater for heating an interior surface of a hollow body of conducting material and adapted to be supported in a tapered holder comprismg an inductor head providing a coil having a single turn dimensioned to be positioned within said hollow body in closely spaced relation thereto and a shank for positioning and supporting said coil in said hollow body and for delivering high frequency power thereto, said shank comprising a pair of closely spaced conductors of large cross section presenting fiat opposed faces to each other to provide a low impedance path for carrying current to said coil, said shank being provided with a tapered outer surface for insertion into the tapered holder, the outer periphery of said inductor head being accurately machined with reference to said tapered shank to provide a construction which may be accurately positioned within said hollow body with minimum clearance.

2. An induction heater as recited in claim I wherein a portion of said shank is of reduced diameter and encircled by an insulating band to clamp said conductors together as a sturdy unitary structure.

3. An electromagnetic induction heater for heating an internal surface of a hollow body of conducting material and adapted to being supported in a tapered holder comprising an accurately machined inductor head providing a single turn coil arranged to be placed within the hollow body in closely spaced relation to the inner surface thereof and a tapered shank for insertion in the tapered holder for positioning and supporting said inductor head within said hollow body and for delivering high frequency power thereto, said coil being of relatively short ax al length and arranged in a plane perpendicular to the axis of the heater and effective to heat a band of said surface substantially equal to the width of the coil whereby the depth of penetration of the heating may be precisely controlled by varying the scanning rate of said coil longitudinally within said hollow body.

4. An electromagnetic induction heater for heating a portion of a hollow body of conducting material near its inner surface comprising a coil having a single turn arranged to be placed within the hollow body in closely spaced relation to the inner surface thereof and a shank for supporting said coil and for delivering high frequency power thereto, said shank comprising a pair of conductors presenting flat opposed faces to each other to provide a low impedance path for carrying current in said coil, and a cluster of tubes arranged in heat conducting relationship within said coil for cooling said coil, said conductors being hollow for carrying coolant to said cluster of tubes.

5. An electromagnetic induction heater for heating the inner surface of a bore formed in a conducting body comprising a tapered holder, a chuck for holding the conducting body in axial alignment with the tapered holder and an induction heater comprising a single turn coil for entering the bore in closely spaced relation thereto and a tapered shank for insertion in said tapered holder for positioning and precisely supporting said coil in said bore, said coil being machined with reference to said tapered shank to provide a construction in which the clearance between the coil and the surface of the bore is minimized for maximum efliciency of heating.

6. An electromagnetic induction heater for heating an interior surface of a hollow body of conducting material and adapted to be supported in a tapered holder comprising an inductor head providing a coil having a single turn dimensioned to be positioned within said hollow body in closely spaced relation thereto and a tapered shank for positioning and supporting said coil in said hollow body, said tapered shank and said inductor head being accurately machined with respect to each other, with said tapered shank serving as the sole means for positioning and supporting said inductor head.

References Cited in the file of this patent FOREIGN PATENTS Great Britain Feb. 17, 1949 

